In the production of package containers for foods, extremely high demands are placed on cleanliness and hygiene, with a view to reducing the population of bacteria in the finished package container. It generally applies that the more the population of bacteria in a package container can be reduced, the longer will be the shelf-life of the packed product, of course on condition that the package container is completely bacteria-proof, so that bacteria cannot penetrate in from the outside after sealing of the package. A special type of package container consists of the so-called sterile or aseptic package containers which are filled with previously sterilized (for example heat-treated) contents such as milk or juice. In the production of package containers of this type, a treatment is required with disinfectant agents, normally hydrogen peroxide (H.sub.2 O.sub.2) in the vaporized or gaseous state in order to ensure that the population of bacteria in the package container has been reduced to a sufficient degree to guarantee, after filling and sealing of the package container, a desired lengthy shelf-life, on the order of several months.
Package containers of the above-mentioned type, i.e. package containers of the disposable type intended for liquid contents such as milk and juice, are normally produced from a packaging laminate which includes a carrier layer of fibrous material, for example paper, which is coated on either side with a thermoplastic material, primarily polyethylene. The packaging laminate may also include other layers, for example gas barrier layers such as aluminium foil or the like. After reforming of the packaging laminate into tubular blanks fitted with a bottom, these blanks are subjected, prior to filling with previously sterilized contents, to a sterilization treatment, i.e. a so-called commercial sterilization, with a view to reducing the population of viable bacteria to a level acceptable for achieving desired product shelf-life. The sterilization normally takes place in that a gaseous or vaporized chemical sterilization container during a sufficient period of time, whereafter the agent is removed by the package container being exposed to a current of hot sterile air until all residues of the employed sterilization agent have reliably been extracted. During this treatment, the individual package container blank is, in prior art apparatuses, enclosed in a chamber which, by the intermediary of channels and valves, is connectible both to a source of sterilization agent and to a source of sterile hot air. The package container blank is moved via a gate into the above-mentioned chamber with the aid of a conveyor, and both filling of the package container and sealing of its upper portion must take place before the package container departs from the sterile area. This requires a relatively large amount of room and the sterile area must, hence, be of relatively large size, with the result that it may be difficult to guarantee that sterility can be maintained at all times. In itself, the conveyor which moves the package containers into and out of the sterile chamber also constitutes an infection risk, since all matter which is displaced from the ambient surroundings of the chamber into the chamber may entrain bacteria. On the whole, it is generally desirable within this art to reduce the degree and intensity of interaction between the chamber and its surroundings as far as is possible, for example by reducing to a minimum the still necessary area of the passages and by always ensuring that the pressure in the sterile chamber is slightly higher than the ambient pressure, so that leakage will always be one-way, from the inside and outwards. Despite the above-mentioned measures, it does happen in prior art apparatuses for treating package container blanks that bacteria may penetrate into the sterile area, which necessitates operational down-time and a specific sterilization, so-called presterilization, of the sterile area before production can be resumed.
The gate and conveyor arrangements which are necessary in prior art apparatuses are also relatively complex, with the result that mechanical problems at times occur and package container blanks become jammed and torn in the sterile chamber. In such an event, it is necessary to open the sterile chamber and manually remove the remains of the package container, and once again clean and presterilize the apparatus, implying a lengthy period of operational down-time during which the entire packaging machine must stand idle.